Mode of Action of Linenscin OC2 against Listeria innocua

Linenscin OC2 is a small hydrophobic substance produced by the orange cheese coryneform bacterium Brevibacterium linens OC2. Linenscin OC2 inhibits growth of gram-negative bacteria with an altered outer membrane permeability and gram-positive bacteria. It is also able to lyse eucaryotic cells. The mode of action of linenscin OC2 on the Listeria innocua cytoplasmic membrane and the effects of environmental parameters were investigated. Addition of low doses of linenscin OC2 resulted in an immediate perturbation of the permeability properties of the cytoplasmic membrane and of the bacterial energetic state. Linenscin OC2 induced a loss of cytoplasmic potassium, depolarization of the cytoplasmic membrane, complete hydrolysis of internal ATP, efflux of inorganic phosphate, and transient increase in oxygen consumption. Potassium loss occurred in the absence of a proton motive force and was severely reduced at low temperatures, presumably as a result of increased ordering of the lipid hydrocarbon chains of the cytoplasmic membrane. We propose that linenscin OC2 interacts with the cytoplasmic membrane and that the permeability changes observed at low doses reflect the formation of pore-like structures in this membrane.     

Activity and purification of linenscin OC2, an antibacterial substance produced by Brevibacterium linens OC2, an orange cheese coryneform bacterium.

An orange cheese coryneform bacterium isolated from the surface of Gruyère of Comté and identified as Brevibacterium linens produces an antimicrobial substance designated linenscin OC2. This compound inhibits gram-positive food-borne pathogens including Staphylococcus aureus and Listeria monocytogenes but is not active against gram-negative bacteria. Linenscin OC2 caused viability loss and lysis of the test organism, Listeria innocua. Electron microscopy showed that linenscin OC2 induces protoplast formation and cell lysis. The native substance is resistant to proteolytic enzymes, heat, and organic solvents and stable over a wide range of pH. The molecular weight of the native linenscin OC2 was estimated by gel chromatography to be over 285,000. Linenscin OC2 was purified by ammonium sulfate precipitation, 2-propanol extraction, and reverse-phase chromatography. Direct detection of antimicrobial activity on a sodium dodecyl sulfate-polyacrylamide gel suggested an apparent molecular mass under 2,412 Da. Molecular mass was determined to be 1,196.7 Da by mass spectrometry. Amino acid composition analysis indicated that linenscin OC2 may contain 12 residues.     

Lipopolysaccharide induces amyloid formation of antimicrobial peptide HAL-2

Lipopolysaccharide (LPS), the important component of the outer membrane of Gram-negative bacteria, contributes to the integrity of the outer membrane and protects the cell against bactericidal agents, including antimicrobial peptides. However, the mechanisms of interaction between antimicrobial peptides and LPS are not clearly understood. Halictines-2 (HAL-2), one of the novel antimicrobial peptides, was isolated from the venom of the eusocial bee Halictus sexcinctus. HAL-2 has exhibited potent antimicrobial activity against Gram-positive and Gram-negative bacteria and even against cancer cells. Here, we studied the interactions between HAL-2 and LPS to elucidate the antibacterial mechanism of HAL-2 in vitro. Our results show that HAL-2 adopts a significant degree of β-strand structure in the presence of LPS. LPS is capable of inducing HAL-2 amyloid formation, which may play a vital role in its antimicrobial activity.     

Bactericidal Activity of Curcumin I Is Associated with Damaging of Bacterial Membrane

Curcumin, an important constituent of turmeric, is known for various biological activities, primarily due to its antioxidant mechanism. The present study focused on the antibacterial activity of curcumin I, a significant component of commercial curcumin, against four genera of bacteria, including those that are Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa). These represent prominent human pathogens, particularly in hospital settings. Our study shows the strong antibacterial potential of curcumin I against all the tested bacteria from Gram-positive as well as Gram-negative groups. The integrity of the bacterial membrane was checked using two differential permeabilization indicating fluorescent probes, namely, propidium iodide and calcein. Both the membrane permeabilization assays confirmed membrane leakage in Gram-negative and Gram-positive bacteria on exposure to curcumin I. In addition, scanning electron microscopy and fluorescence microscopy were employed to confirm the membrane damages in bacterial cells on exposure to curcumin I. The present study confirms the broad-spectrum antibacterial nature of curcumin I, and its membrane damaging property. Findings from this study could provide impetus for further research on curcumin I regarding its antibiotic potential against rapidly emerging bacterial pathogens.     

Membrane interaction and antibacterial properties of chensinin-1, an antimicrobial peptide with atypical structural features from the skin of Rana chensinensis

Many antimicrobial peptides from amphibian skin have been purified and structurally characterized and may be developed as therapeutic agents. Here we describe the antibacterial properties and membrane interaction of chensinin-1, a cationic arginine/histidine-rich antimicrobial peptide, from the skin secretions of Rana chensinensis. The amino acid composition, sequence, and atypical structure of chensinin-1 differ from other known antimicrobial peptides from amphibian skin. Chensinin-1 exhibited selective antimicrobial activity against Gram-positive bacteria, was inactive against Gram-negative bacteria, and had no hemolytic activity on human erythrocytes. The CD spectra for chensinin-1 indicated that the peptide adopted an aperiodic structure in water and a conformational structure with 20?% β-strands, 8?% α-helices, and the remaining majority of random coils in the trifluoroethanol or SDS solutions. Time-kill kinetics against Gram-positive Bacillus cereus demonstrated that chensinin-1 was rapidly bactericidal at 2× MIC and PAE was found to be >5?h. Chensinin-1 caused rapid and large dye leakage from negatively charged model vesicles. Furthermore, membrane permeation assays on intact B. cereus indicated that chensinin-1 induced membrane depolarization in less than 1?min and followed to damage the integrity of the cytoplasmic membrane and resulted in efflux of molecules from cytoplasma. Hence, the primary target of chensinin-1 action was the cytoplasmic membrane of bacteria. Chensinin-1 was unable to overcome bacterial resistance imposed by the lipopolysaccharide leaflet, the major constituent of the outer membrane of Gram-negative bacteria. Lipopolysaccharide induced oligomerization of chensinin-1, thus preventing its translocation across the outer membrane.     

The Lipopeptide Antibiotic Paenibacterin Binds to the Bacterial Outer Membrane and Exerts Bactericidal Activity through Cytoplasmic Membrane Damage

Paenibacterin is a broad-spectrum lipopeptide antimicrobial agent produced by Paenibacillus thiaminolyticus OSY-SE. The compound consists of a cyclic 13-residue peptide and an N-terminal C₁₅ fatty acyl chain. The mechanism of action of paenibacterin against Escherichia coli and Staphylococcus aureus was investigated in this study. The cationic lipopeptide paenibacterin showed a strong affinity for the negatively charged lipopolysaccharides (LPS) from the outer membrane of Gram-negative bacteria. Addition of LPS (100 μg/ml) completely eliminated the antimicrobial activity of paenibacterin against E. coli. The electrostatic interaction between paenibacterin and LPS may have displaced the divalent cations on the LPS network and thus facilitated the uptake of antibiotic into Gram-negative cells. Paenibacterin also damaged the bacterial cytoplasmic membrane, as evidenced by the depolarization of membrane potential and leakage of intracellular potassium ions from cells of E. coli and S. aureus. Therefore, the bactericidal activity of paenibacterin is attributed to disruption of the outer membrane of Gram-negative bacteria and damage of the cytoplasmic membrane of both Gram-negative and Gram-positive bacteria. Despite the evidence of membrane damage, this study does not rule out additional bactericidal mechanisms potentially exerted by paenibacterin.     

Cell-Wall Interactions and the Selective Bacteriostatic Activity of a Miniature Oligo-Acyl-Lysyl

The oligo-acyl-lysyl, C_12(ω7)K-β₁₂, is comprised of only three Lys residues. Despite its small size, it exhibits potent bacteriostatic activity against Gram-positive bacteria, but it is ∼10-fold less potent against Gram-negative bacteria. We followed the interactions of C_12(ω7)K-β₁₂ from its initial contact with the bacterial surface across the cell wall down to the cytoplasmic membrane. Binding to anionic lipids, as well as to negatively charged LPS and LTA, occurs with very high affinity. The C_12(ω7)K-β₁₂ does not cross the outer membrane of Gram-negative bacteria; rather, it achieves its action by depositing on the LPS layer, promoting surface adhesion and blocking passage of solutes. In Gram-positive bacteria, the thick peptidoglycan layer containing LTA allows passage of C_12(ω7)K-β₁₂ and promotes its accumulation in the small periplasm. From that location it is then driven to the membrane by strong electrostatic interactions. Despite its high potency against Gram-positive bacteria, this agent is not capable of efficiently breaking down the permeability barrier of the cytoplasmic membrane or of reaching an intracellular target, as suggested by the fact that it does not interact with DNA.     

Polymyxin E Induces Rapid Paenibacillus polymyxa Death by Damaging Cell Membrane while Ca2+ Can Protect Cells from Damage

Polymyxin E, produced by Paenibacillus polymyxa, is an important antibiotic normally against Gram-negative pathogens. In this study, we found that polymyxin E can kill its producer P. polymyxa, a Gram-positive bacterium, by disrupting its cell membrane. Membrane damage was clearly revealed by detecting the leakage of intracellular molecules. The observation using scanning electron microscopy also supported that polymyxin E can destroy the cell membrane and cause an extensive cell surface alteration. On the other hand, divalent cations can give protection against polymyxin E. Compared with Mg²⁺, Ca²⁺ can more effectively alleviate polymyxin E-induced damage to the cell membrane, thus remarkably increasing the P. polymyxa survival. Our findings would shed light on a not yet described bactericidal mechanism of polymyxin E against Gram-positive bacteria and more importantly the nature of limited fermentation output of polymyxin E from P. polymyxa.     

Molecular recognition of lipopolysaccharide by the lantibiotic nisin

Nisin is a lanthionine antimicrobial effective against diverse Gram-positive bacteria and is used as a food preservative worldwide. Its action is mediated by pyrophosphate recognition of the bacterial cell wall receptors lipid II and undecaprenyl pyrophosphate. Nisin/receptor complexes disrupt cytoplasmic membranes, inhibit cell wall synthesis and dysregulate bacterial cell division. Gram-negative bacteria are much more tolerant to antimicrobials including nisin. In contrast to Gram-positives, Gram-negative bacteria possess an outer membrane, the major constituent of which is lipopolysaccharide (LPS). This contains surface exposed phosphate and pyrophosphate groups and hence can be targeted by nisin. Here we describe the impact of LPS on membrane stability in response to nisin and the molecular interactions occurring between nisin and membrane-embedded LPS from different Gram-negative bacteria. Dye release from liposomes shows enhanced susceptibility to nisin in the presence of LPS, particularly rough LPS chemotypes that lack an O-antigen whereas LPS from microorganisms sharing similar ecological niches with antimicrobial producers provides only modest enhancement. Increased susceptibility was observed with LPS from pathogenic Klebsiella pneumoniae compared to LPS from enteropathogenic Salmonella enterica and gut commensal Escherichia coli. LPS from Brucella melitensis, an intra-cellular pathogen which is adapted to invade professional and non-professional phagocytes, appears to be refractory to nisin. Molecular complex formation between nisin and LPS was studied by solid state MAS NMR and revealed complex formation between nisin and LPS from most organisms investigated except B. melitensis. LPS/nisin complex formation was confirmed in outer membrane extracts from E. coli.     

Synergistic action of Galleria mellonella anionic peptide 2 and lysozyme against Gram-negative bacteria

Lysozyme and antimicrobial peptides are key factors of the humoral immune response in insects. In the present work lysozyme and anionic defense peptide (GMAP2) were isolated from the hemolymph of the greater wax moth Galleria mellonella and their antibacterial activity was investigated. Adsorption of G. mellonella lysozyme on the cell surface of Gram-positive and Gram-negative bacteria was demonstrated using immunoblotting with anti-G. mellonella lysozyme antibodies. Lysozyme effectively inhibited the growth of selected Gram-positive bacteria, which was accompanied by serious alterations of the cell surface, as revealed by atomic force microscopy (AFM) imaging. G. mellonella lysozyme used in concentrations found in the hemolymph of naive and immunized larvae, perforated also the Escherichia coli cell membrane and the level of such perforation was considerably increased by GMAP2. GMAP2 used alone did not perforate E. coli cells nor influence lysozyme muramidase activity. However, the peptide induced a decrease in the turgor pressure of the bacterial cell. Moreover, in the samples of bacteria treated with a mixture of lysozyme and GMAP2 the sodium chloride crystals were found, suggesting disturbance of ion transport across the membrane leading to cell disruption. These results clearly indicated the synergistic action of G. mellonella lysozyme and anionic peptide 2 against Gram-negative bacteria. The reported results suggested that, thanks to immune factors constitutively present in hemolymph, G. mellonella larvae are to some extent protected against infection caused by Gram-negative bacteria.     

Outer Membrane Permeabilization Is an Essential Step in the Killing of Gram-Negative Bacteria by the Lectin RegIIIβ

The C-type lectin RegIIIβ can kill certain Gram-positive and Gram-negative bacteria. The susceptibility of S. Typhimurium depends on the bacterial growth phase, i.e., bacteria from the logarithmic growth phase do bind RegIIIβ and are subsequently killed. Lipid A is one of the bacterial targets for RegIIIβ. However, at the molecular level, it is not understood how RegIIIβ interacts with and kills Gram-negative bacteria. Here, we show that RegIIIβ interacts with Gram-negative bacteria in two distinct steps. Initially, it binds to surface-exposed lipid A. The lipid A can be shielded by the O-antigen of lipopolysaccharide (LPS), as indicated by the exquisite susceptibility of wbaP mutants to RegIIIβ-mediated killing. Increased cell viability after incubation with an anti-lipid A antibody also supports this conclusion. This RegIIIβ-binding permeabilizes the outer membrane to hydrophobic dyes like Ethidium bromide or to bulky bacteriolytic enzymes like lysozyme. Conversely, compromising the outer membrane integrity by the mild detergent Triton X-100 enhances the antibacterial effect of RegIIIβ. Based on our observations, we conclude that RegIIIβ interacts with Gram-negative bacteria in two subsequent steps. Initially, it binds to the outer membrane thus leading to outer membrane permeabilization. This initial step is necessary for RegIIIβ to reach a second, still not well understood target site (presumably localized in the periplasm or the cytoplasmic membrane), thereby triggering bacterial death. This provides novel insights into the outer membrane-step of the bactericidal mechanism of RegIIIβ.     

Studies on the Mode of Membrane Interaction of C-terminally Amidated Brevinin1 HYba1 and 2 Peptides Against Bacteria

In this study, we investigated the possible mode of action of two C-terminally amidated novel peptides identified from the frog skin on both Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Vibrio cholerae). The results indicate that the peptides initially induce membrane depolarization followed by pore formation in a concentration-dependent manner. A microscopic examination revealed the fact that the peptides are capable of destroying bacterial cells physically. The activity of these peptides against Gram-negative bacteria was dependent on the presence of divalent cations (Ca²⁺ and Mg²⁺) but not in Gram-positive bacteria. This study also emphasizes that the endemic frogs of the Western Ghats may provide a valuable source of its skin peptides having the potential for further improvement as lead drug molecules.     

Dual mechanism of bacterial lethality for a cationic sequence-random copolymer that mimics host-defense antimicrobial peptides

Flexible sequence-random polymers containing cationic and lipophilic subunits that act as functional mimics of host-defense peptides have recently been reported. We used bacteria and lipid vesicles to study one such polymer, having an average length of 21 residues, that is active against both Gram-positive and Gram-negative bacteria. At low concentrations, this polymer is able to permeabilize model anionic membranes that mimic the lipid composition of Escherichia coli, Staphylococcus aureus, or Bacillus subtilis but is ineffective against model zwitterionic membranes, which explains its low hemolytic activity. The polymer is capable of binding to negatively charged vesicles, inducing segregation of anionic lipids. The appearance of anionic lipid-rich domains results in formation of phase-boundary defects through which leakage can occur. We had earlier proposed such a mechanism of membrane disruption for another antimicrobial agent. Experiments with the mutant E. coli ML-35p indicate that permeabilization is biphasic: at low concentrations, the polymer permeabilizes the outer and inner membranes; at higher polymer concentrations, permeabilization of the outer membrane is progressively diminished, while the inner membrane remains unaffected. Experiments with wild-type E. coli K12 show that the polymer blocks passage of solutes into the intermembrane space at high concentrations. Cell membrane integrity in E. coli K12 and S. aureus exhibits biphasic dependence on polymer concentration. Isothermal titration calorimetry indicates that the polymer associates with the negatively charged lipopolysaccharide of Gram-negative bacteria and with the lipoteichoic acid of Gram-positive bacteria. We propose that this polymer has two mechanisms of antibacterial action, one predominating at low concentrations of polymer and the other predominating at high concentrations.     

A Thermostable Salmonella Phage Endolysin,Lys68, with Broad Bactericidal Properties against Gram-Negative Pathogens in Presence of Weak Acids

Resistance rates are increasing among several problematic Gram-negative pathogens, a fact that has encouraged the development of new antimicrobial agents. This paper characterizes a Salmonella phage endolysin (Lys68) and demonstrates its potential antimicrobial effectiveness when combined with organic acids towards Gram-negative pathogens. Biochemical characterization reveals that Lys68 is more active at pH 7.0, maintaining 76.7% of its activity when stored at 4°C for two months. Thermostability tests showed that Lys68 is only completely inactivated upon exposure to 100°C for 30 min, and circular dichroism analysis demonstrated the ability to refold into its original conformation upon thermal denaturation. It was shown that Lys68 is able to lyse a wide panel of Gram-negative bacteria (13 different species) in combination with the outer membrane permeabilizers EDTA, citric and malic acid. While the EDTA/Lys68 combination only inactivated Pseudomonas strains, the use of citric or malic acid broadened Lys68 antibacterial effect to other Gram-negative pathogens (lytic activity against 9 and 11 species, respectively). Particularly against Salmonella Typhimurium LT2, the combinatory effect of malic or citric acid with Lys68 led to approximately 3 to 5 log reductions in bacterial load/CFUs after 2 hours, respectively, and was also able to reduce stationary-phase cells and bacterial biofilms by approximately 1 log. The broad killing capacity of malic/citric acid-Lys68 is explained by the destabilization and major disruptions of the cell outer membrane integrity due to the acidity caused by the organic acids and a relatively high muralytic activity of Lys68 at low pH. Lys68 demonstrates good (thermo)stability properties that combined with different outer membrane permeabilizers, could become useful to combat Gram-negative pathogens in agricultural, food and medical industry.     

The introduction of l-phenylalanine into antimicrobial peptide protonectin enhances the selective antibacterial activity of its derivative phe-Prt against Gram-positive bacteria

Protonectin was a typical amphiphilic antimicrobial peptide with potent antimicrobial activity against Gram-positive and Gram-negative bacteria. In the present study, when its eleventh amino acid in the sequence was substituted by phenylalanine, the analog named phe-Prt showed potent antimicrobial activity against Gram-positive bacteria, but no antimicrobial activity against Gram-negative bacteria, indicating a significant selectivity between Gram-positive bacteria and Gram-negative bacteria. However, when Gram-negative bacteria were incubated with EDTA, the bacteria were susceptible to phe-Prt. Next, the binding effect of phe-Prt with LPS was determined. Our result showed that LPS could hamper the bactericidal activity of phe-Prt against Gram-positive bacteria. The result of zeta potential assay further confirmed the binding effect of phe-Prt with LPS for it could neutralize the surface charge of E. coli and LPS. Then, the effect of phe-Prt on the integrity of outer membrane of Gram-negative bacteria was determined. Our results showed that phe-Prt had a much weaker disturbance to the outer membrane of Gram-negative bacteria than the parent peptide protonectin. In summary, the introduction of l-phenylalanine into the sequence of antimicrobial peptide protonectin made phe-Prt show significant selectivity against Gram-positive bacteria, which could partly be attributed to the delay effect of LPS for phe-Prt to access to cell membrane. Although further study is still needed to clarify the exact mechanism of selectivity, the present study provided a strategy to develop antimicrobial peptides with selectivity toward Gram-positive and Gram-negative bacteria.

     

Evaluation of a series of 2-napthamide derivatives as inhibitors of the drug efflux pump AcrB for the reversal of antimicrobial resistance

Drug efflux pumps confer multidrug resistance to dangerous pathogens which makes these pumps important drug targets. We have synthesised a novel series of compounds based on a 2-naphthamide pharmacore aimed at inhibiting the efflux pumps from Gram-negative bacteria. The archeatypical transporter AcrB from Escherichia coli was used as model efflux pump as AcrB is widely conserved throughout Gram-negative organisms. The compounds were tested for their antibacterial action, ability to potentiate the action of antibiotics and for their ability to inhibit Nile Red efflux by AcrB. None of the compounds were antimicrobial against E. coli wild type cells. Most of the compounds were able to inhibit Nile Red efflux indicating that they are substrates of the AcrB efflux pump. Three compounds were able to synergise with antibiotics and reverse resistance in the resistant phenotype. Compound A3, 4-(isopentyloxy)-2-naphthamide, reduced the MICs of erythromycin and chloramphenicol to the MIC levels of the drug sensitive strain that lacks an efflux pump. A3 had no effect on the MIC of the non-substrate rifampicin indicating that this compound acts specifically through the AcrB efflux pump. A3 also does not act through non-specific mechanisms such as outer membrane or inner membrane permeabilisation and is not cytotoxic against mammalian cell lines. Therefore, we have designed and synthesised a novel chemical compound with great potential to further optimisation as inhibitor of drug efflux pumps.     

Bacteriocins with anti-MRSA activity produced by water and soil isolated bacteria

Among a thousand of bacteria isolated from forty-three samples, ten isolated bacteria strain WARY1-6, WARY9-1, WARY9-2, WARY6-6, SOPB1, WARY9-10, WARY7-4, WASM9-25, SOPB8-91 and WAS14 with antimicrobial activity against methicillin resistantStaphylococcus aureus (MRSA) were selected for further study. The activity of crude active supernatant (CAS) from these isolated bacteria was completely lost after treated with pronase E, chymotrypsin and trypsin demonstrating its proteinaceous nature. These isolated bacteria could be regarded as bacteriocin producing bacteria (BAC). It was also found that CAS from five Gram-positive isolated bacteria strain WARY1-6, WARY9-1, WARY9-2, WARY6-6 and WASM9-25 showed a broad range of inhibition as they can inhibit at least five Gram-positive and two Gram-negative test microorganisms. Two Gram-negative bacteria can be regarded as BAC with a broad range against both Gram-positive and Gram-negative test bacteria. These seven isolated bacteria can be regarded as BAC with a broad range of antagonistic activity. One isolated bacteria strain SOPB1 harboured a single large plasmid name pSOPB1-19. Its bacteriocin production was associated with plasmid as analysed by plasmid extraction and curing experiment. The strain SOPB1 was identified asBacillus sphaericus according to its 16s rRNA gene sequence. Its bacteriocin was heat stable up to 121 °C, 15 min and active within the pH range of 6–9.     

Evidence for a two-metal-ion mechanism in the cytidyltransferase KdsB, an enzyme involved in lipopolysaccharide biosynthesis

Lipopolysaccharide (LPS) is located on the surface of Gram-negative bacteria and is responsible for maintaining outer membrane stability, which is a prerequisite for cell survival. Furthermore, it represents an important barrier against hostile environmental factors such as antimicrobial peptides and the complement cascade during Gram-negative infections. The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) is an integral part of LPS and plays a key role in LPS functionality. Prior to its incorporation into the LPS molecule, Kdo has to be activated by the CMP-Kdo synthetase (CKS). Based on the presence of a single Mg²⁺ ion in the active site, detailed models of the reaction mechanism of CKS have been developed previously. Recently, a two-metal-ion hypothesis suggested the involvement of two Mg²⁺ ions in Kdo activation. To further investigate the mechanistic aspects of Kdo activation, we kinetically characterized the CKS from the hyperthermophilic organism Aquifex aeolicus. In addition, we determined the crystal structure of this enzyme at a resolution of 2.10 Å and provide evidence that two Mg²⁺ ions are part of the active site of the enzyme.     

The cathelicidin-like peptide derived from panda genome is a potential antimicrobial peptide

A novel cathelicidin-like antimicrobial peptide was identified by mining genome of panda. This peptide (cathelicidin-AM) was synthesized. It showed potential antimicrobial activities against wide spectrum of microorganisms including Gram-negative and -positive bacteria, and fungi. It had similar antimicrobial abilities against both standard and clinically isolated drug-resistant strains. Cathelicidin-AM could rapidly exert its antibacterial activities. It just took less than 1 h to kill all Staphylococcus sciuri at the concentration of 2, 4 or 10 times of minimal inhibitory concentration (MIC) while clindamycin took 6 h. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analysis indicated that cathelicidin-AM killed bacteria by directly affecting bacterial cell wall and membrane. Phylogenetic analysis revealed that the panda cathelicidin had the nearest evolution relationship with dog cathelicidin. The current work provides a novel cathelicidin-like peptide with strong antimicrobial abilities.